varying vec3 vertex_light_position;varying vec3 vertex_normal;void main(){                // Calculate the normal value for this vertex, in world coordinates (multiply by gl_NormalMatrix)    vertex_normal = normalize(gl_NormalMatrix * gl_Normal);       // Calculate the light position for this vertex    vertex_light_position = normalize(gl_LightSource[0].position.xyz);       // Set the front color to the color passed through with glColor*f    gl_FrontColor = gl_Color;       // Set the position of the current vertex    gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;}